High burning rate propellants have been formulated with very fine oxidizer particle sizes; however, the very fine particle sizes (less than 20 microns) result in decreased usable pot life. The usable pot life is the time available for accomplishing the processing steps of mixing and casting propellant before the propellant loses its fluid nature.
Earlier work in propellant technology has resulted in development of reaction products formed from reacting di- or tri-functional aziridinyl phosphine oxides or their derivatives with polyfunctional carboxylic acids. These reaction products have been used to coat inorganic oxidizer particles which are used in propellant compositions, and when so used, the coated particles enhance the mechanical properties of the propellant. Patent application Ser. No. 851,137, filed July 30, 1969, now U.S. Pat. No 3,762,972, and its divisional application Ser. No. 105,938, filed Jan. 12, 1971, and now U.S. Pat. No. 3,745,074, teach the process for preparation, the products produced, the products coated on ammonium perchlorate, and the coated ammonium perchlorate in propellant compositions. When the propellant compositions containing the described coated ammonium perchlorate are cured, the mechanical properties, particularly the strain at break and tensile strength, are greatly improved at 77.degree. F as well as at -40.degree. F. The propellant compositions contained, generally a 50--50 blend of very fine particle size ammonium perchlorate (17 micron nominal diameter) and larger particle size ammonium perchlorate (200 micron nominal diameter). The processing of this type blend of oxidizer particles can be accomplished without major problems relating to mixing and pot life.
The advantage of using substantially all very fine ammonium perchlorate in propellant compositions has been demonstrated with respect to improved burning rates. The problems encountered when using very fine ammonium perchlorate, however, which relate to mixing and retaining proper pot life have required much effort to be devoted to determining what can be done to permit using high percentage of fine ammonium perchlorate while retaining proper pot life for mixing and casting the propellant.
Therefore, an object of this invention is to provide compounds for extending pot life of isocyanate curable propellant compositions which employ very fine oxidizer.
Another object of this invention is to provide isocyanate curable propellant compositions having improved pot life to provide sufficient time for the mixing and casting thereof.